This invention relates to continuously variable transmissions and more particularly, it concerns a speed ratio adjusting system for such transmissions in which torque is transmitted by friction between two bodies having variable relative radii at two points of rolling friction contact.
The disclosures of U.S. Pat. Nos. Re. 29,328, Re. 30,981 and 4,112,779 contain several embodiments of continuously variable nutational traction drive transmissions in which three frame supported working bodies operate to transmit a mechanical power input to a rotatable output at infinitely variable output/input speed ratios within the design range of the transmission. For purposes of definition in this background discussion as well as in the ensuing detailed description of the present invention and in the appended claims, the three working bodies may be termed, respectively, an "alpha body" which is supported by the transmission frame to be concentric with a first axis, a "beta body" which is supported by the alpha body to be concentric with a second axis inclined with respect to and intersecting the first axis at a point of axes intersection, and an "omega body" carried by the frame to be concentric also with the first axis. Although any one of these three bodies may be rotatable on the respective axes with which they are concentric, one of the three is held against rotation to provide a reaction torque whereas the other two bodies are rotatable and coupled either directly or by gearing to the respective input and output shafting of the transmission. In a preferred mode of operation, power input drives the alpha body in rotation to carry the beta body in rolling frictional engagement with a grounded omega body. Speed ratio adjustment is most commonly though not exclusively adjusted by using a pair of rings as the grounded omega body and shifting the rings along the first transmission axis. In this way the radius ratio of the constant radius rings and the variable radius bioconical beta body may be varied in continuous or stepless fashion.
All embodiments of nutational drive transmissions disclosed in these U.S. patents may be characterized as axially oriented in the sense that the angle between the first and second intersecting axes is a relatively small acute angle so that the first and second axes always lie within the two points rolling friction engagement between the beta and omega bodies. In a more recent development of nutational traction drive transmissions exemplified by the disclosure of U.S. Pat. No. 4,630,494 the angle between the first and second transmission axes is increased so that the points of rolling friction contact lie within the sector subtended by that angle. As a result, the beta body and its axis are supported in a generally radial orientation by the alpha body. Such radially orientated nutational traction drive transmissions exhibit significantly increased speed ratio variation and other geometric characteristics which make them especially desirable for automotive application whereas the prior axially oriented transmissions are more suited to use on heavy equipment.
In the geometry of radially orientated nutational traction drive transmissions, the omega body is again grounded but takes the form of spaced plate or dish-shaped members against which oppositely diverging, generally conical members of the beta body engage at two points of rolling friction contact. In one embodiment of such transmission, the beta body is supported by the alpha body at a fixed angle of intersection with normal forces for rolling friction engagement developed by a ramp system supporting the omega plates against the nutating beta body. Speed ratio variation in this form of transmission is effected by moving the cone members of the beta body inwardly or outwardly along the beta body axis and thus take advantage of the radial variation in both the omega plates and in the beta body cones to attain an expanded range of transmission speed ratios. Heretofore, and as disclosed in the aforementioned allowed patent application, movement of the cones along the beta body axis has been accomplished primarily by hydraulic piston/cylinder units which suffer the disadvantage of being less precise than desirable in controlling movement of the cone members, complicated by sealing requirements and perhaps more importantly, inefficient from the standpoint of energy losses principally in pumping the hydraulic fluid to the pressures required for such control systems.